FIG. 1 shows a magnetic portion of a conventional superconductive NMR imaging diagnostic apparatus, comprising a superconductive main coil 2 contained in a cryostat 1, inclined magnetic field coils 3, 4 and 5 disposed inside the main coil 2, a bobbin 6, and a bed unit 7, so that an examinee is positioned within the bobbin 6. The inclined magnetic field coils comprising two pairs of X-direction coils 3, 3 . . . , each having a saddle-like shape and disposed transversely, two pairs of Y-direction coils 4, 4 . . . , each having a saddle-like shape and disposed vertically, and a pair of Z-direction solenoid-type coils 5, 5 disposed longitudinally, are mounted on the bobbin 6 formed of a non-conductive material.
The coils 3, 4, 5 are mounted on the bobbin 6 in such a manner that the windings 9, 9 . . . of each coil, as shown in FIG. 2, are secured to the bobbin 6 by a band 10, such as a glass fiber tape, or the windings 9, 9 . . . , as shown in FIG. 3, are press-contacted by bolts 12, 12 . . . through a pressure plate 11.
In such an apparatus, the inclined magnetic coils 3, 4 and 5 are excited by the intense DC magnetic field generated by the main coil 2, at which time a current flowing in the coils, as shown in FIG. 4(a), is of pulse-like wave form, so that the coils 3, 4 and 5 each generates an electromagnetic mechanical force, thereby vibrating as the current varies as shown in FIG. 4(b).
The electromagnetic mechanical force generated in the coils 3, 4 and 5 is similar in wave form to the current shown in FIG. 4(a). Hence, the frequency component of the mechanical force is distributed over a wide frequency domain of DC to kHz, vibrations and noises caused thereby having the similar frequency component.
The conventional inclined magnetic field coil, whose windings are fixed directly to the bobbin, transmits its vibrations to the bobbin directly. As a result, a problem has occurred in that noises emitted together with the vibrations of the bobbin cause pain to the examinee positioned inside the bobbin.